The pharmaceutically important diterpene lactone ginkgolides are products of secondary metabolism in Ginkgo biloba (G. biloba) plants. With over 3000 publications on these compounds since 2001 and annual sales of ˜$250 million in the US alone, G. biloba extract and its constituents are currently among the most studied and sold phytochemical worldwide1. Ginkgolides exhibit bioactivities as antagonists of platelet-activating factor, γ-aminobutyric acid (GABA), and glycine receptors, resulting in therapeutics that are administered for improvement in vascular function, inhibition of thrombosis and embolism, and neuroprotective function2-5. Moreover, their potential as cancer therapeutics is under investigation6. Currently, the availability of ginkgolides is limited because less than 5 p.p.m of products can be obtained from leaf extract'. Furthermore, the growth of G. biloba is also extremely slow. Scalable production routes via plant cell culture and chemical synthesis have been explored; however, they are still far from industrial application. Ginkgolides yield from plant cell culture is relatively low (˜40 mg/L)7 and synthetic methods require more than 20 steps8.
The success of fermentation technology to produce many fine and commodity chemicals has inspired the heterologous production of several plant terpenoids using microbial hosts9-13. In plants, secondary metabolite pathways are genetically programmed and regulated (transcriptionally and post-translationally) so that these chemicals are only synthesized as needed14, 15. A particular branch pathway is not designed to overproduce a certain metabolite, but rather, so that the overall metabolism works in concert. A successful microbial production platform, on the other hand, requires that an imported pathway generate a high production yield. Metabolic engineering to increase flux through an engineered plant-derived pathway has been shown to improve terpenoid production12, 13, 16.